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United States Patent |
5,254,350
|
Barrow
,   et al.
|
October 19, 1993
|
Method of preparing a thromboplastin extract
Abstract
A process for preparing a thromboplastin extract including extracting a
powdered thromboplastin source in an aqueous solution having a metal ion
chelator, and separating the powder in solution into sedimented powder and
supernatant thromboplastin extract is disclosed. The supernatant
thromboplastin extract is mixed with calcium ions, and may be mixed with
one or more of a stabilizer and a preservative, to prepare thromboplastin
reagent.
Inventors:
|
Barrow; David A. (Sour Lake, TX);
Rullman; Richard L. (Beaumont, TX)
|
Assignee:
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Helena Laboratories Corporation (Beaumont, TX)
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Appl. No.:
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733325 |
Filed:
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July 22, 1991 |
Current U.S. Class: |
424/570; 424/583; 435/13; 514/2; 514/21; 530/381 |
Intern'l Class: |
A61K 035/30 |
Field of Search: |
424/570,583
514/2,21
530/381
435/13
|
References Cited
U.S. Patent Documents
3522148 | Jul., 1970 | Adam, Jr. et al. | 435/13.
|
4416812 | Nov., 1983 | Becker et al. | 260/112.
|
4784944 | Nov., 1988 | Kolde | 435/13.
|
Other References
Hubbard et al., BA82:20346, 1986.
Hubbard et al., "Inhibition of Tissue Thromboplastin-Mediated Blood
Coagulation," Thrombosis Research 42:489-498 (1986).
|
Primary Examiner: Robinson; Douglas W.
Assistant Examiner: Witz; Jean C.
Attorney, Agent or Firm: Spencer, Frank & Schneider
Claims
We claim:
1. A process for preparing a thromboplastin extract comprising:
a) providing a powdered thromboplastin source;
b) extracting said powdered brain thromboplastin source in an aqueous
solution comprising a metal ion chelator;
c) separating said powdered brain thromboplastin source in aqueous solution
into sedimented powder and supernatant thromboplastin extract; and
d) isolating said supernatant thromboplastin extract.
2. The process for preparing a thromboplastin extract according to claim 1,
wherein said powdered brain thromboplastin source is rabbit brain powder.
3. The process for preparing a thromboplastin extract according to claim 1,
wherein said metal ion chelator is EDTA.
4. The process for preparing a thromboplastin extract according to claim 3,
wherein said EDTA is present in amount of from about 0.1 to about 5 mM
EDTA.
5. The process for preparing a thromboplastin extract according to claim 4,
wherein said EDTA is present in an amount of about 1 mM EDTA.
6. The process for preparing a thromboplastin extract according to claim 1,
wherein said separating step is by centrifugation.
7. The process for preparing a thromboplastin extract according to claim 1,
further comprising:
e) freeze drying said supernatant thromboplastin extract.
8. The process for preparing a thromboplastin extract according to claim 1,
wherein said sedimented powder includes said metal ion chelator.
9. The process for preparing a thromboplastin extract according to claim 1,
wherein said supernatant thromboplastin extract includes said metal ion
chelator.
10. The process for preparing a thromboplastin extract according to claim
9, wherein said metal ion chelator is EDTA.
11. The process for preparing a thromboplastin extract according to claim
1, wherein said metal ion chelator is EDTA.
12. The process for preparing a thromboplastin extract according to claim
11, wherein said EDTA is present in amounts of from about 0.1 to about 5
mM EDTA.
13. The process for preparing a thromboplastin extract according to claim
12, wherein said EDTA is present in an amount of about 1 mM EDTA.
14. The process for preparing a thromboplastin extract according to claim
1, wherein said metal ion chelator is EGTA.
15. The process for preparing a thromboplastin extract according to claim
7, wherein said metal ion chelator is EGTA.
16. The process for preparing a thromboplastin extract according to claim
7, wherein said powdered brain thromboplastin source is rabbit brain
powder.
17. A process for preparing a thromboplastin extract comprising an aqueous
thromboplastin extract of brain powder comprising:
a) providing brain tissue;
b) homogenizing said brain tissue in excess acetone to produce a slurry;
c) drying said slurry to produce brain powder;
d) extracting said brain powder in an aqueous solution comprising a metal
ion chelator;
e) separating said brain powder in aqueous solution into sedimented brain
powder and supernatant thromboplastin extract; and
f) isolating said supernatant thromboplastin extract.
18. The process for preparing a thromboplastin extract according to claim
17, wherein said metal ion chelator is EDTA.
19. The process for preparing a thromboplastin extract according to claim
18, wherein said EDTA is present in amounts of from about 0.1 to about 5
mM EDTA.
20. The process for preparing a thromboplastin extract according to claim
19, wherein said EDTA is present in an amount of about 1 mM EDTA.
21. The process for preparing a thromboplastin extract according to claim
17, wherein said separating step is by centrifugation.
22. The process for preparing a thromboplastin extract according to claim
17, further comprising:
g) freeze drying said supernatant thromboplastin extract.
23. The process for preparing a thromboplastin extract according to claim
17, wherein said sedimented brain powder includes said metal ion chelator.
24. The process for preparing a thromboplastin extract according to claim
17, wherein said supernatant thromboplastin extract includes said metal
ion chelator.
25. The process for preparing a thromboplastin extract according to claim
22, wherein said metal ion chelator is EDTA.
26. The process for preparing a thromboplastin extract according to claim
25, wherein said EDTA is present in amounts of from about 0.1 to about 5
mM EDTA.
27. The process for preparing a thromboplastin extract according to claim
26, wherein said EDTA is present in an amount of about 1 mM EDTA.
28. The process for preparing a thromboplastin extract according to claim
17, wherein said metal ion chelator is EGTA.
29. The process for preparing a thromboplastin extract according to claim
22, wherein said metal ion chelator is EGTA.
30. The process for preparing a thromboplastin extract according to claim
17, wherein said brain tissue is rabbit brain tissue.
31. The process for preparing a thromboplastin extract according to claim
22, wherein said brain tissue is rabbit brain tissue.
32. The process for preparing a thromboplastin extract according to claim
24, wherein said metal ion chelator is EDTA.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to thromboplastin extracts and reagents, and more
particularly to thromboplastin extracts and reagents including a chelator.
2. Technology Background
Blood coagulation involves a succession of reactions leading to the
formation of fibrin. Fibrin is the protein that holds blood clots
together. Fibrin is formed from a soluble precursor, fibrinogen, by the
protease thrombin. Thrombin is generated during clotting from an inactive
precursor, prothrombin (Factor II), through one of two mechanisms known as
the extrinsic and intrinsic pathways. The extrinsic pathway comes into
action in response to tissue injury, and involves the participation of
blood clotting factors V, VII, and X. The extrinsic and intrinsic pathways
converge in a final common pathway for the thrombin-catalyzed conversion
of fibrinogen to the fibrin clot.
Clinical tests of blood coagulation include the prothrombin time test. The
prothrombin time test is a measure of the extrinsic pathway of blood
coagulation. Prothrombin time, hereinafter (PT), measures the time
elapsing until plasma clots in the presence of a tissue thromboplastin
reagent. The test is performed by adding a tissue thromboplastin reagent
to the plasma and determining the time necessary for coagulation. The
thromboplastin reagent, along with factor VII, activates factor X to
X.sub.a (active factor X) in the presence of factor V.sub.a (active factor
V), Ca.sup.2+, and platelet phospholipids. Prothrombin is converted to
thrombin, which in turn catalyzes the formation of fibrin from fibrinogen.
Thus, a deficiency of factor II, V, VII, or X or a severe deficiency of
fibrinogen will prolong the PT. Normal plasma contains factors VII and X;
therefore, if normal plasma corrects the PT, the defect must be due to a
deficiency of one of those two factors.
Blood coagulation requires calcium. Since calcium is present in plasma
itself, anticoagulants such as sodium citrate or EDTA are often placed in
the vials that hold plasma to block its spontaneous coagulation. The
plasma together with sodium citrate or EDTA as an anticoagulant is
referred to as anticoagulated plasma. Calcium ions in a saturating amount
are added according to the prior art to overcome the sodium citrate or
EDTA and to prevent the sodium citrate or EDTA from affecting PT time.
The prothrombin time test can monitor coumarin therapy for maintenance of
the therapeutic range. The coumarin drugs are used clinically to impede
blood coagulation in thrombotic states, including heart disease. They
inhibit the vitamin K-dependent synthesis of factors II, VII, IX and X.
U.S. Pat. No. 3,522,148, dated Jul. 28, 1970, to Adam, Jr. discloses a
stabilized thromboplastin reagent including a mixture of a saline extract
of acetone-dried rabbit brain tissue and a sodium salt, and an equal
volume of aqueous solution of calcium chloride. Adam, Jr. also discloses a
stabilized thromboplastin reagent including a mixture of a saline extract
of acetone-dried rabbit brain tissue and an equal volume of a calcium salt
of a sugar acid. U.S. Pat. No. 4,784,944, dated Nov. 15, 1988, to Kolde,
H. J. discloses thromboplastin obtained from human placenta.
The three general steps in preparing a thromboplastin reagent include
preparing a powdered thromboplastin source, converting the powdered
thromboplastin source into a thromboplastin extract, and preparing a
useful thromboplastin reagent from the thromboplastin extract.
Sources of thromboplastin include rabbit brain, human placenta, bovine
brain, ox brain, human brain, and thromboplastin produced by recombinant
DNA technology. Powdered thromboplastin sources include rabbit brain
powder, powdered human placenta, powdered bovine brain, powdered ox brain,
powdered human brain, and powdered thromboplastin produced by recombinant
DNA technology.
Rabbit brain powder is prepared according to the prior art by homogenizing
whole rabbit brains stripped of attached blood vessels with excess
acetone, and drying the slurry under vacuum. Rabbit brain powder is
commercially available.
Powdered human placenta is prepared according to the prior art in a manner
similar to the preparation of rabbit brain powder.
Rabbit brain powder is converted into a useful thromboplastin extract
according to the prior art by a procedure that involves extraction of the
powder in warm saline solution and centrifugation to remove the sedimented
brain powder, leaving a supernatant extract rich in thromboplastin. U.S.
Pat. No. 4,416,812, dated Nov. 22, 1983, to Becker et al. discloses using
calcium ions during extraction.
The thromboplastin reagent is then prepared from the extract by combining
the extract with stabilizers and preservatives and one of various calcium
salts to produce a bulk reagent, and then usually lyophilizing the reagent
for long-term storage.
A problem which limits the effectiveness of the prothrombin time test is
that chemical variation of the thromboplastin extract and the
thromboplastin reagent formulations can alter the PT. The PT for normal
human plasma based on the use of fresh basic raw material, rabbit brain
powder, is the standard value for comparison. Physicians in the United
States relying on PT results for screening and diagnostic purposes
generally expect normal human plasma to clot within 12 seconds after
contact with a standardized thromboplastin reagent that is lyophilized and
reconstituted. The in-process extract solutions before lyophilization and
reconstitution into a standardized thromboplastin reagent are required to
provide a PT of less than or equal to 11 seconds. From time to time, for
as yet unknown reasons, rabbit brain powder from commercial suppliers may
vary from its normal quality, and produce extracts unsuitable for reagent
preparation by conventional methods because they yield long PTs for normal
human plasma.
One way to accomplish standardized results of the prothrombin time test is
to provide extracts and reagents that have a consistently lower PT of
normal human plasma from lot to lot. Another way to achieve comparability
is standardization in reference to a particular factor sensitivity.
"Sensitive" reagents need not provide a lower PT value. However, it is
beneficial for even so-called "sensitive" reagents to provide a lower PT
value so that the effects of the variables that are modified to achieve a
particular factor sensitivity do not prolong the reagent's PT of normal
human to so great an extent that testing becomes impractical with
automated instrumentation.
Accordingly, it is the main object of the present invention to provide a
process for preparing a thromboplastin extract and reagent which overcomes
the aforementioned disadvantages. Specifically, it is a principal object
of this invention to provide extract and a thromboplastin reagent that
consistently provides a lower PT of normal human plasma from lot to lot.
Another object of the invention is to improve a wide variety of powdered
thromboplastin sources within a species such as rabbit brain powders all
to a standard level of PT, thus allowing for improved lot-to-lot
thromboplastin reagent reproducibility, so that data can be compared for
meaningful, consistent results.
Another object of the invention is to provide a thromboplastin reagent from
a raw powdered thromboplastin source such as rabbit brain powder that may
not otherwise be useful for preparing a standardized thromboplastin
reagent.
These objects and others which will become apparent as the specification
progresses are accomplished by the invention.
SUMMARY OF THE INVENTION
The present invention provides a process for preparing a thromboplastin
extract from a thromboplastin source by providing a powdered
thromboplastin source, extracting said powdered thromboplastin source in
an aqueous solution comprising a metal ion chelator, separating the
powdered thromboplastin source in aqueous solution into sedimented powder
and supernatant thromboplastin extract having the thromboplastin and
isolating the supernatant thromboplastin extract. The process may further
include freeze drying the supernatant thromboplastin extract. The
supernatant thromboplastin extract prepared by this process may further
include the metal ion chelator, or the metal ion chelator may precipitate.
The thromboplastin source may be rabbit brain tissue or human placenta,
for example, and the powdered thromboplastin source may be rabbit brain
powder or powdered human placenta, for example.
The present invention provides a process for preparing a thromboplastin
reagent by mixing the supernatant thromboplastin extract prepared by the
above process with calcium ions. One or more of a stabilizer and a
preservative may be added to the extract. The thromboplastin reagent
produced by this process may but need not contain the metal ion chelator.
The present invention further provides a process for preparing a
thromboplastin reagent comprising an aqueous thromboplastin extract of a
powdered thromboplastin source including a metal ion chelator, and calcium
ions by mixing a thromboplastin extract including an aqueous
thromboplastin source and a metal ion chelator, with calcium ions. One or
more of a stabilizer and a preservative may be added to the extract.
The present invention further provides a thromboplastin extract including
an aqueous thromboplastin extract of a powdered thromboplastin source and
a metal ion chelator. The present invention also provides a thromboplastin
reagent including an aqueous thromboplastin extract of a powdered
thromboplastin source and a metal ion chelator, and calcium ions, and may
further include one or more of a stabilizer and a preservative.
DETAILED DESCRIPTION OF THE INVENTION
All original sources of thromboplastin may be used. Examples of sources of
thromboplastin are human placenta, rabbit brain, bovine brain, ox brain,
and human brain. Thromboplastin produced by recombinant DNA technology may
be used. Preferably, the source of thromboplastin is rabbit brain.
Rabbit brain powder is commercially available and it may be isolated
according to a standard technique by removing whole brains stripped of
attached blood vessels from, for example, New Zealand White rabbits,
homogenizing the rabbit whole brains in excess acetone in a Waring blender
to produce a slurry, and drying the slurry under vacuum to produce rabbit
brain powder which is stable when stored under vacuum at -20.degree. C.
Powdered bovine brain, powdered x brain, powdered human brain, powdered
thromboplastin produced by recombinant DNA technology, and powdered human
placenta are prepared in a manner according to the prior art similar to
the preparation of rabbit brain powder.
The powdered thromboplastin source such as rabbit brain powder or human
placenta powder is then extracted in an aqueous solution to prepare
thromboplastin extract. The aqueous solution may be a warm saline
solution. To solve the problem of lot-to-lot variations in PT time of
normal plasma, the inventors have discovered that a metal ion chelator
should be added during the extraction. According to the invention, the
thromboplastin extract is prepared by extracting the powdered
thromboplastin source in an aqueous solution including a metal ion
chelator, separating the powdered thromboplastin source into sedimented
powder and supernatant thromboplastin extract having thromboplastin, and
isolating the supernatant thromboplastin extract. The separating step may
be by centrifuging. The thromboplastin extract may then be freeze dried.
The supernatant thromboplastin extract made by this process comprises an
aqueous thromboplastin extract of rabbit brain powder or other source of
thromboplastin such as human placenta powder, and it may further include a
metal ion chelator. Alternately, the metal ion may precipitate and the
extract does not include the metal ion chelator.
Any metal ion chelator that functions similarly to
ethylenediaminetetraacetic acid (EDTA) in binding/chelation of calcium
ions or other metal ions may be used for practicing the invention.
Specific examples of metal ion chelators that may be used in the present
invention are citrate, salts of citrate, EGTA
(Ethylene-bis(oxyethylenenitrilo)]tetraacetic acid, and salts of EGTA.
Preferably, the metal ion chelator is ethylenediaminetetraacetic acid
(EDTA) or a salt of EDTA. According to the invention, during extraction of
a powdered thromboplastin source, a small amount of metal ion chelator is
included. Approximately at least 0.1 mM of metal ion chelator is added to
the aqueous solution of the extraction. Preferably, 0.5-5.0 mM of metal
ion chelator is added to the aqueous solution. Most preferably, 1.0 mM of
metal ion chelator is added to the aqueous solution. The metal ion
chelator stock solution may be pH neutralized according to common
laboratory practice. Preferably, a small amount of pH neutralized,
concentrated metal ion chelator is delivered to the extraction solution
prior to adding the powdered source of thromboplastin.
The thromboplastin reagent may then be prepared according to the invention
by mixing the thromboplastin extract prepared by the above process with
calcium ions. The thromboplastin reagent prepared by this process may but
need not include the metal ion chelator in the final reagent.
The present invention further provides a process for preparing a
thromboplastin reagent comprising an aqueous thromboplastin extract of a
powdered thromboplastin source including a metal ion chelator, and calcium
ions by mixing a thromboplastin extract including an aqueous
thromboplastin source and a metal ion chelator, with calcium ions. One or
more of a stabilizer and a preservative may be added to the extract.
Any source of calcium ions may be used for practicing the invention.
Specifically, a calcium salt such as calcium chloride may be used. Calcium
salts of sugar acids such as calcium tartrate, calcium gluconate, calcium
citrate, or calcium lactate may be substituted for calcium chloride.
The thromboplastin extract according to the invention comprises an aqueous
thromboplastin extract of a powdered thromboplastin source and a metal ion
chelator.
The thromboplastin reagent according to the invention comprises a
thromboplastin extract of rabbit brain powder or other source of a
powdered thromboplastin source and a metal ion chelator, and calcium ions.
The thromboplastin reagent contains calcium ions at a concentration of
5-20 mM, preferably 12 mM.
The thromboplastin reagent may contain a metal ion chelator if calcium ions
are present in sufficient concentration to overcome the metal ion chelator
level in addition to the amount of sodium citrate or EDTA present in the
anticoagulated plasma. Calcium ions in a saturating amount are added to
overcome the metal ion chelator, and the sodium citrate or EDTA, present
in the anticoagulated plasma.
The thromboplastin reagent may further include a stabilizer. Any stabilizer
that functions to maintain the activity of the thromboplastin reagent may
be used for practicing the invention. Specifically, a buffer salt such as
a Good buffer, or Tris (trishydroxymethylaminomethane) may be used. The
stabilizer may be, for example, PIPES (Piperazine-N,N-bis
(2-ethane-sulfonic acid, 1.5 sodium salt)); Imidazole; MOPSO
(3-(N-Morpholino)-2-hydroxypropanesulfonic acid); BES
(N,N-bis-(Hydroxyethyl)-2-aminoethanesulfonic acid); MOPS
(3-(N-Morpholino) propanesulfonic acid); TES
(N-tris-(Hydroxymethyl)-methyl-2-aminoethanesulfonic acid); HEPES
(N-2-Hydroxyethyl piperazine-N-2-ethanesulfonic acid); DIPSO
(3-[N-Bis(hydroxyethyl)amino]-2-hydroxypropanesulfonic acid); TAPSO
(3-[N-tris(Hydroxymethyl)methylamino]-2-hydroxypropanesulfonic acid);
POPSO (Piperazine-N,N'-bis(2-hydroxy-propanesulfonic acid)); HEPPSO
(N-Hydroxyethyl piperazine-N'-2-hydroxypropanesulfonic acid); Tricine
(N-Tris [hydroxymethyl]methyl-glycine); Bicine
(N,N'-Bis-(2-hydroxyethyl)-glycine); and TAPS (3-[N-tris-{Hydroxymethyl)
methylamino]-propanesulfonic acid).
The thromboplastin reagent may further include a preservative. Any
preservative that functions to prevent the growth of microorganisms that
would damage the thromboplastin reagent may be used for practicing the
invention, such as antibacterial and antifungal compositions.
Specifically, sodium azide, thimerosal, BHA, and BHT may be used.
Preferably the preservative is thimerosal.
While not wishing to be bound by any theory, Applicants believe that the
mechanism of their invention involves the known biochemical inhibitor of
the Factor X activator complex called the Extrinsic Pathway Inhibitor
(EPI). The inhibitory binding of EPI is mediated by calcium ions and can
be reversed by chelators, such as EDTA or similar metal ion chelators.
Break up of this EPI complex by chelators appears to allow isolation of
thromboplastin free from the inhibitory EPI, assuming that the EPI
partitions into the pelleted rabbit brain residue upon separation, for
example, centrifugation. This latter assumption is reasonable since EPI is
also known as lipoprotein associated coagulation inhibitor (LACI).
The following examples are offered by way of illustration and not by way of
limitation.
EXAMPLE 1
A thromboplastin reagent was prepared from commercially available rabbit
brain powder according to the invention as follows:
A 10.0 g amount of rabbit brain powder was extracted using a 1.0 mM EDTA
solution (198 mL of 0.7% saline and 2 mL of 100 mM EDTA) (for a total of
200 mL).
The solution was extracted at 50.degree. C, spun, filtered, and thimerosal
(0.14 g/L) was added. Testing was done using a glycine (4.6%) and calcium
chloride (16 mM) solution: one part extract, three parts Ca.sup.2+
/glycine solution.
Tests revealed the following prothrombin time (PT) values.
Using normal control plasma (Helena Laboratories, Norm-Trol): 10.7 secs,
10.8 secs, 10.1 secs and 10.2 secs.
Using abnormal control plasma missing calcium-dependent Factors II, VII, IX
and X (Helena Laboratories, Ab-Trol I): 17.0 secs and 17.4 secs.
COMPARATIVE EXAMPLE 2
A thromboplastin reagent was prepared from the same commercially available
rabbit brain powder in Example 1 according to the following process:
A 10.0 g amount of rabbit brain powder was extracted using 0.7% saline (for
a total of 200 mL).
The solution was extracted at 50.degree. C., spun, filtered and thimerosal
added (0.14 g/L). Testing was done using a glycine (4.6%) and calcium
chloride (16 mM) solution: one part extract, three parts Ca.sup.2+
/glycine solution.
Tests revealed the following prothrombin time (PT) values.
Using normal control plasma (Helena Laboratories, Norm-Trol): 12.2 secs and
12.5 secs.
Using abnormal control plasma missing calcium-dependent Factors II, VII, IX
and X (Helena Laboratories, Ab-Trol I): 20.1 secs and 20.9 secs.
As the above examples show, the process according to the invention in
Example 1 using EDTA provides an unexpected improvement over the process
in Comparative Example 2 not using EDTA.
In the above examples, prothrombin time (PT) was determined according to
the following procedure.
Using the Helena Dataclot-2 of Helena Laboratories, which is an
electro-mechanical coagulation instrument, PTs were performed with normal
control plasma, (Helena Laboratories, Norm-Trol) and abnormal control
plasma missing calcium-dependent Factors II, VII, IX, and X (Helena
Laboratories, Ab-Trol I), and used the following volumes: 0.1 mL control
plasma plus 0.2 mL thromboplastin reagent with calcium. The control plasma
and the thromboplastin reagent with calcium were separately warmed to
37.degree. C., then 0.2 mL of the thromboplastin reagent with calcium ions
was pipetted into a reaction cup holding 0.1 mL of the control plasma, and
the time required for clot formation was noted.
It will be understood that the above description of the present invention
is susceptible to various modifications, changes and adaptations, and the
same are intended to be comprehended within the meaning and range of
equivalence of the appended claims.
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